Propulsion referred to as “hybrid”, namely propulsion combining a solid fuel with a liquid oxidant, has been known for over 50 years. It was developed chiefly for rocket motor propulsion because it does not use ambient air to supply an oxidizing agent. Its main characteristic is a high level of thrust even in the anaerobic phase, thanks to use of a liquid oxidant.
In most instances, the motor 11 is made up of a hermetic chamber 12 in which is stored, for example, a brick of powder 13 (see FIG. 1). Made in the brick of powder 13 are one or more ducts 14 (which form part of the volume of the combustion chamber) into which an oxidant is injected, in this instance via an injector 15 situated in the upper part of the combustion chamber. The liquid oxidant is injected into the ducts 14 at a high temperature (typically >800 K) under the effect of a pyrotechnic igniter and/or a catalytic decomposition. Under the effect of the temperature, the brick of powder 13 vaporizes at the walls of the ducts 14 and begins to react (combust) with the oxidant. The expansion of the gases thus generated (through a nozzle 16) generates a thrust.
Once combustion has been initiated, the system is sustained with the injection of oxidant at ambient temperature (typically 300 K) and the vaporization of the solid/powder fuel.
During the course of combustion, the brick of powder 13 is consumed and the size of the ducts 14 increases. This type of operation is termed “radial combustion” on account of the radial increase in the size of the ducts.
Such a hybrid motor is, for example, described in Rockwell patent document U.S. Pat. No. 5,101,623 (1992).
This type of motor has the disadvantage of a progressive increase in the size of the ducts 14 over time, and therefore in the volume of the combustion chamber which consequently leads to a significant variation in the thrust provided by the motor over the course of time.
This type of motor is also ill-suited to large volumes of powder/solid brick because it requires, in order to limit the variation in volume of the combustion chamber during combustion, the use of a duct (and a brick of powder/solid) that is very long (by comparison with its diameter). This type of constraint, which leads to motors which are long and slender, is somewhat incompatible with use on a satellite.